|Publication number||US6501611 B1|
|Application number||US 09/300,293|
|Publication date||Dec 31, 2002|
|Filing date||Apr 27, 1999|
|Priority date||Apr 27, 1999|
|Publication number||09300293, 300293, US 6501611 B1, US 6501611B1, US-B1-6501611, US6501611 B1, US6501611B1|
|Inventors||Robert Yuan-Shih Li|
|Original Assignee||International Business Machines Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (22), Referenced by (15), Classifications (29), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of Invention
This invention relates to magnetic memory devices and, more particularly, to recovery of data when there is an error during a read operation.
2. Description of Prior Art
A magnetic memory device, such as a disk drive or a tape drive, typically has a magnetic head or transducer and a magnetic medium formatted into multiple data tracks. The magnetic medium is moved past a station where the transducer is located. The transducer is positioned to write or read data to or from addressable locations contained along the tracks.
The magnetic memory device also includes a read/write signal processing section that processes a read signal produced by the transducer before handing it over to a computer or other device that requested the data. The signal processing section includes a preamplifier for amplifying the read signal.
The signal to noise ratio (SNR) is a significant determinant of the read back performance of the magnetic memory device. For a given memory capacity design, a minimum SNR is usually required to meet the device's soft error rate target. A high amplitude output signal from the head can saturate the preamplifier to produce a distorted signal that increases noise, thereby resulting in a degraded SNR. If the amplitude of output signal from the head is too low for the voltage gain amplifier in the channel:, the SNR can also be degraded. Both of these conditions can lead to higher bit error rate. It is known that, due to bit crowding, the amplitude of the read signal varies with track location. For example, when the head is positioned above an inner track on a magnetic disk medium, the amplitude is low. When it is positioned above an outer track, the amplitude is high.
U.S. Pat. No. 4,772,964 deals with this situation by varying the gain of the preamplifier according to track position. A computer provides a gain value for each position of the transducer to the preamplifier. The gain value selects the value of a resistor that determines gain of the preamplifier. Thus, the gain is reduced for a high amplitude signal and is increased for a low amplitude signal. The gain is also adjusted based on the ambient temperature in which the magnetic memory device is situated. The temperature measurement is not needed when the ambient temperature is controlled to a constant temperature.
U.S. Pat. No. 5,519,548 discloses a procedure that uses read channel noise to calibrate amplifier gain and discrimination thresholds in the read/write signal processing circuitry of a magnetic memory device. The calibration procedure achieves a final threshold value that ensures that the read signal must exceed a predetermined signal to noise ratio before the read signal is accepted as valid. The calibration procedure is performed before searching for a head alignment reference signal on the magnetic medium.
Neither of the aforementioned patents addresses recovery of errors caused by variations in spacing or gap between the head and the disk surface due to debris, asperity of the disk surface or due to temperature and pressure change in the hard disk drive.
It is an object of the present invention to provide an apparatus that recovers the data of a read signal that is in error due to variations in head to disk gap caused by disk surface asperity or hard disk drive temperature/pressure change and to thermal asperity events.
It is another object of the present invention to provide a method of recovering the data of a read signal that is in error due to variations in head to disk gap caused by disk surface asperity or hard disk drive temperature/pressure change and to thermal asperity events.
It is another object of the present invention to provide a memory medium that stores a program that controls the signal processing section of a read/write channel to recover the data of a read signal that is in error due to variations in head to disk gap caused by disk surface asperity or hard disk drive temperature/pressure change and to thermal asperity events.
A method for recovering data according to the present invention is operative during a read operation of a magnetic memory device when an error is detected. The magnetic memory device has a moving magnetic medium upon which data is stored at addressable locations, a transducer for reading the data to produce a read signal and an adjustable gain amplifier for amplifying the read signal. The transducer is spaced from the moving medium by a normal gap distance.
The data recovery method of the present invention involves producing a first read signal by reading a first data from one of the addressable locations. Next, the first read signal is examined for an error. If an error is detected, the method tests for a variation from the normal gap distance. If a variation is found, the amplifier gain is adjusted dependent upon the variation. Next, the first data is reread to produce a second read signal. It is then determined if the second read signal is error free. If the second read signal is error free, the first data is recovered from the second read signal and provided to an output of the magnetic memory device.
The variation from the normal gap distance can be caused by an asperity of the magnetic medium surface, such as an accumulation of debris or a roughness or unevenness. In such case, the variation is a decrease from the normal gap distance that results in a higher amplitude read signal that saturates the amplifier. For this situation, the amplifier gain is decreased.
The variation from the normal gap distance can be caused by a change in disk temperature from a reference temperature, such as the medium temperature at the time of manufacture, and the moving medium. If the temperature increases, the gap decreases and the amplifier gain is decreased. If the temperature decreases, the gap increases and the amplifier gain is increased.
The data recovery apparatus and memory medium of the present invention involve the procedure described above for the data recovery method.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure and:
FIG. 1 is a block diagram of a magnetic memory device according to the present invention;
FIG. 2 is a flow diagram of the operation of the FIG. 1 magnetic memory device; and
FIG. 3 is a flow diagram of the data recovery procedure of the FIG. 2 flow diagram.
With reference to FIG. 1, there is provided a magnetic storage device generally represented by numeral 10. Although the data recovery apparatus, method and memory medium of the present invention is applicable to either magnetic disk or magnetic tape memory devices, magnetic memory device 10 is shown, by way of example, as a magnetic disk memory device.
Magnetic memory device 10 has a magnetic disk 12 that is rotated by a spindle 14 driven by a motor (not shown). Magnetic disk 12 rotates in the direction shown by arrow 16. A temperature sensor 18 is located in proximity to spindle 14 and magnetic disk 12 to sense the temperature of magnetic disk 12. A transducer 20 is arranged to write and/or read data to or from addressable locations on magnetic disk 12 in a conventional manner. Transducer 20 is preferably a magnetoresistive (MR) head.
Transducer 20 is electrically coupled with a read/write signal processing assembly 21. Transducer 20 and read/write signal processing assembly 21 may be physically housed in an arm assembly (not shown). The arm assembly can be moved under control of read/write signal processing assembly 21 and motors (not shown) to position transducer 20 to write and/or read data to or from different cylindrical tracks along magnetic disk 12.
Read/write signal processing assembly 21 includes a preamplifier 22, a threshold detector 24, a read/write channel 26, a control computer 30, a gain adjuster 28 and an interface 40. Control computer 30 controls the positioning of transducer 20 to an addressable location along magnetic disk 12 and the operation of preamplifier 22, read/write channel 26 and gain adjuster 28 during read and write operations.
The data recovery feature of the present invention is concerned with the recovery of data when an error is detected in a read signal produced by transducer 20. In particular, these errors arise from read signals that have an amplitude that is too low to be detected or that is so high as to saturate preamplifier 22. In either case an error is detected.
A high or a low amplitude of a read signal can arise when transducer 20 varies in spacing to magnetic disk 12 from a normal gap distance g. The gap distance g is selected during design for an optimum read signal output from transducer 20. However various factors can contribute to variances from the gap distance g that can produce the aforementioned errors in the read signal. One such factor involves the surface of magnetic disk 12 that may contain an asperity due to an accumulation of debris or to a roughness or unevenness. An asperity condition causes the MR head to heat frictionally or to cool through conduction and, for this reason, is, called thermal asperity. If data is read while a thermal asperity condition is present, the read signal amplitude will include high amplitude spikes or transients that may saturate preamplifier 22.
Another factor involves changes in temperature of magnetic disk 12. During a normal read operation, an air flow caused by rotation of magnetic disk 12 provides a fly lift to transducer 20 that elevates it to approximately the selected gap distance g. If the temperature of disk 20 increases from the reference temperature (say, by 10° C.), the air above the rotating disk becomes hotter. This causes the fly height to decrease enough to result in a high enough read signal amplitude to saturate preamplifier 22, thereby causing an error. If the disk temperature decreases, the fly height increases and the read signal amplitude decreases. If the decrease is significant, the signal amplitude could be low enough to cause an error. Depending on the bearing design, altitude from sea level or barometric pressure may have similar effects as temperature on the magnetic spacing. The reference temperature may, for example, be the prevailing temperature of disk 12 during manufacture.
To determine if a thermal asperity condition is present, threshold detector 24 is provided to detect transient signals that exceed a threshold for a time duration long enough (for example, one or more bit times) to cause an error in a read signal. The threshold value is set to a value in a range from the amplitude of an average read signal expected for the operating range of preamplifier 22 to the amplitude level that just saturates preamplifier 22. The output of threshold detector 24 is applied to read/write channel 26 and ultimately to control computer 30 for use in the data recovery procedure.
The disk temperature is sensed by temperature sensor 18. The output of temperature sensor 18 is applied to read/write channel 26 and ultimately to control computer 30 for use in the data recovery procedure. Read/write channel 26 includes an analog to digital converter to convert analog signals, such as the temperature signal output of temperature sensor 18, into a digital signal for use by control computer 30.
Preamplifier 22 has a variable gain that is controlled by control computer 30 and gain adjuster 28. For example, the gain of preamplifier 22 may suitably be determined by the value of a variable resistor connected in a gain control circuit of preamplifier 22. The variable resistor may comprise a resistor network that is configurable into a resistor having a desired gain value in response to a digital gain value provided by control computer 30. Thus, gain adjuster 28 may include a decoder that decodes the digital gain value to provide one or more signals that operate one or more switches to configure the resistor network to have the desired gain value.
Control computer 30 includes a processor 31, a memory 32, an EPROM 36 and a communication port 37, all of which are interconnected via a computer bus 35. Generally, processor 31 operates under the control of programs stored in memory 32 to control the various tasks involved in read and write operations of magnetic memory device 10 in accordance with various design parameters contained in EPROM 36. To control these tasks, processor communicates with read/write channel 26 and interface 40 by way of communication port 37.
A data recovery program 33 is stored in memory 32. Data recovery program 33 is operable to control processor 31 to conduct a data recovery procedure in accordance with the present invention. Data recovery program 33 may be stored on a memory medium 34 for installation in memory 32 by way of input/output I/O devices 38. I/O devices 38 may be coupled with bus 35 at the time of assembly of read/write signal processing assembly 21 or at a later time via connectors (not shown) available to the outside world.
Referring to FIG. 2, a system program 50 begins at step 51 when the power is turned on for magnetic memory device 10. At step 52, a test is performed for the presence of a command. If no command is present, step 52 is periodically repeated until a command is found. When a command is found, step 53 determines if it is a read command. If not, it is classified as another command, such as a write command. Step 54 processes the other command. After step 54 is completed, step 52 resumes its test for a command.
If step 53 determines the command to be a read command, step 55 then determines if the read signal is okay. If so, step 60 returns the read data to interface 40. If the read signal is not okay (i. e., there is a read error), the data recovery program 33 is entered at step 56. When the data recovery program has been run, step 57 determines if the read data has been recovered. If so, the data is returned at step 60 to interface 40. If step 57 determines that the data has not been recovered, step 58 posts an unrecoverable message and logs an error. The system program is then exited at step 59 and remedial action taken.
Referring to FIG. 3, data recovery program begins with step 80 where normal data recovery processing is conducted. At step 81, it is determined if a thermal asperity condition has been detected. That is, the output of threshold detector 24 is examined for the presence of a thermal asperity condition. If there is a thermal asperity condition, step 82 reduces the gain of preamplifier 22 to prevent the thermal asperity from saturating preamplifier 22. The data is reread at step 83. At step 84, it is determined if the data has been recovered. If so, step 85 exits the data recovery program to step 57 of system program 50 in FIG. 2. If step 84 determines that the data is not recovered, step 86 continues the remainder of the data recovery steps that are not pertinent to the present invention. When these steps are completed, step 87 exits the data recovery program to step 57 of system program 50 in FIG. 2.
If step 81 determines that there is no thermal asperity condition, step 88 then determines if the disk temperature is greater than the reference temperature plus a threshold (for example, 10° C.). If the disk temperature is not greater, step 91 determines if the disk temperature is less than the reference temperature minus a threshold (for example, 10° C.). If the disk temperature is not lesser, there is no meaningful variance from the gap distance g due to either a thermal asperity or to a temperature change. Step 86 then continues with the further data recovery steps as described above.
If step 88 determines that there has been a disk temperature increase above the reference temperature by the threshold, the preamplifier gain is reduced at step 90. On the other hand, if step 91 determines that there has been a disk temperature decrease below the reference temperature by the threshold, the preamplifier gain is increased at step 90. After the gain adjustment by either step 90 or step 92, the data is reread by step 93. The next step 94 determines if the data has been recovered. If the data has been recovered, step 85 exits data recovery program 33 to step 57 of system program 50 in FIG. 2.
If step 94 determines that the data is not recovered, step 95 adjusts the equalization of read/write assembly 21 as by making adjustments for variations in pulse width of the read signal. The data is then reread. Step 96 determines if the data has been recovered. If the data has been recovered, step 85 exits data recovery program 33 to step 57 of system program 50 in FIG. 2. If the data has not been recovered by step 95, step 86 continues with the further DRP steps as discussed above.
The present invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as defined in the appended claims. For example, the data recovery procedure, though described herein for one gain selection try, may employ more gain selection tries for either the thermal asperity condition or the disk temperature change condition before step 86 is performed in FIG. 3.
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|U.S. Classification||360/67, G9B/20.053, 360/25, 360/75, G9B/5, G9B/20.009, G9B/5.024, G9B/5.033, 360/53, 360/46|
|International Classification||G11B5/012, G11B20/10, G11B5/00, G11B5/09, G11B33/14, G11B20/18|
|Cooperative Classification||G11B2005/0016, G11B5/00, G11B20/1833, G11B2020/183, G11B5/09, G11B5/012, G11B33/1406, G11B20/10|
|European Classification||G11B20/18D, G11B5/012, G11B5/00, G11B20/10, G11B5/09|
|Apr 27, 1999||AS||Assignment|
Owner name: INTERNATIONAL BUSINESS MACHINES CORPORATION, NEW Y
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:LI, ROBERT YUAN-SHIH;REEL/FRAME:009931/0114
Effective date: 19990426
|Jan 9, 2006||FPAY||Fee payment|
Year of fee payment: 4
|Aug 9, 2010||REMI||Maintenance fee reminder mailed|
|Dec 31, 2010||LAPS||Lapse for failure to pay maintenance fees|
|Feb 22, 2011||FP||Expired due to failure to pay maintenance fee|
Effective date: 20101231